Sulfonated copolyimides: influence of structural parameters on gas separation properties Original Research Article

Structure-properties relationships in terms of gas transport have been established for a large series of sulfonated copolyimides. The permeability and diffusion coefficients of different gases (H2, O2, CO2, N2) differing by their size and interaction capacity towards the polymers have been determined. CO2 sorption experiments have also been carried out allowing a direct determination of the solubility coefficients. The analysis of the transport parameters as a function of the copolyimides structure and composition underlines the predominant role of the non-sulfonated sequences and shows that the permeability is mainly governed by the diffusion coefficient. A large range of permeability values can thus be obtained by varying the nature and the content of the non-sulfonated diamine in the copolyimides and for some copolymers, H2 and CO2 permeability values are similar. Furthermore, O2/N2 selectivity coefficients determined for all the membranes are located near the Robeson curve. As a consequence, some systems, notably those based on (CARDO/ODA) diamines mixture, present a good selectivity/permeability balance.